The goals of this project are to determine the molecular mechanism of adhesion among cells from vertebrate embryos and to use specific molecular probes to analyze the role of cell adhesion in the formation of tissues during development. Our studies have four major objectives: 1) to continue our work on the identification and purification of molecules directly involved in cell adhesion; 2) to characterize these molecules in terms of their chemical and structural properties; 3) to localize and quantitate the molecules in a variety of chick and mouse tissues, in different regions of the same tissue, and with respect to specialized areas of the cell surface membrane; and 4) to investigate the function of cell adhesion molecules in developing tissues by specificaly perturbing their ability to participate in the formation of cell-cell bonds. Many of these studies will utilize an immunologically-based approach that we have developed, in which cell surface molecules involved in adhesion are initially identified through antibodies that inhibit binding between single cells. Specific antibodies prepared against these molecules can then be used to localize and quantitate them, and to perturb their function during the complex interactions that occur in developing tissues. In addition, we will use micro-chemical techniques to analyze the structure of a 140,000 Mr cell adhesion molecule identified in our earlier studies. By determining the partial amino acid sequence of this protein, it should be possible to determine whether it is evolutionarily related to other proteins associated with recognition functions, and whether there is micro-heterogeneity in its primary structure. Our present studies have focused on nerve tissues from chick embryos. By extending them to other chick tissues and to those of inbred mice, we intend to test whether our results are applicable to embryogenesis in general, and to specific developmental defects that have been identified in mutant mice.